Good Points
In npp I, the L1 compressor has to be commended as being just about the best sounding compressor/limiter available as a plugin. It's easy to learn, setup and use. It's also easy to squash the hell out of something and have it sound totally natural. Unless you have some ultra high end compre$$ors in your rig, chances are you've never used compression this transparent before. It certainly never fails to get used on all my pop and dance mixes.
npp II really shines in it's maxbass plugin. It's like an aural exciter for bass, and is quite effective at giving your mixes a bit of extra ultra low end without getting muddy, boomy or obtrusive. Very handy for dance/club music as you'd expect, but useful for other genres too.Bad Points
It's hard to find anything bad to say about these plugins, I've already mentioned the two best plugins in the group. The others are less remarkable, but still worthy additions.
If you bought npp 1&2, plus antares autotune and steinbug, excuse me, steinberg's ;)freefilter, you'd have a formidable arsenal at your disposal that would raise the quality of your production greatly.